The polyamides industry uses a whole range of monomers consisting of long-chain ω-amino acids, commonly termed Nylon, which are characterized by the length of methylene chain (—CH2)n separating two amide functions -CO—NH—. Known, accordingly, are nylon 6, nylon 6-6, nylon 6-10, nylon 7, nylon 8, nylon 9, nylon 11, and nylon 13, etc. The “higher” nylons 11 and 13, for example, which use ω-amino acids as monomer, occupy a separate place in this class, insofar as they are synthesized not from petroleum-derived products (C2 to C4 olefins, cycloalkanes or benzene), but from fatty acids/esters which are present in natural oils.
One example of a process using a fatty acid as starting material is that of the preparation of fatty nitriles and/or amines from fatty acids extracted from plant or animal oils. This process is described in the Kirk-Othmer encyclopedia, vol. 2, 4th edition, page 411. The fatty amine is obtained in a number of steps. The first step involves methanolysis or hydrolysis of a plant oil or of an animal fat, producing, respectively, the methyl ester of a fatty acid, or a fatty acid. The methyl ester of the fatty acid may subsequently be hydrolyzed to form the fatty acid. The fatty acid is subsequently converted into nitrile by reaction with ammonia, and finally into amine by hydrogenation of the resultant nitrile.
Within the field of chemistry, moreover, present environmental developments are resulting in preference being given to the exploitation of natural raw materials originating from a renewable source. It is for this reason that certain research and development studies have been taken up for the purpose of industrial development of processes using fatty acids/esters as starting material for preparation of these ω-amino acid monomers.
The main studies have looked at the synthesis of 9-amino nonanoic acid, the precursor to Nylon 9, from oleic acid of natural origin. With regard to this monomer, it is possible to cite the work “n-Nylons, Their Synthesis, Structure and Properties”-1997, published by J. Wiley and Sons, in which section 2.9 (pages 381 to 389) is devoted to 9-Nylon.
Industrially, for the preparation of polyamide polymerization monomers, there are only few examples of processes using natural oils as starting material. One of the rare examples of an industrial process using a fatty acid as starting material is the preparation process, from the methyl ester of ricinoleic acid, extracted from castor oil, of 11-amino undecanoic acid, which forms the basis for the synthesis of Rilsan 11®. This process is described in the work “Les Procédés de Pétrochimie” by A. Chauvel et al., published by Editions TECHNIP (1986). The 11-amino undecanoic acid is obtained in a number of steps. The first involves a methanolysis of the castor oil in a basic medium, producing methyl ricinoleate, which is subsequently subjected to pyrolysis to give heptanaldehyde on the one hand and methyl undecylenate on the other. The latter is converted into acid form by hydrolysis. The acid formed is subsequently subjected to hydrobromination, to give the ω-brominated acid, which is converted by ammonolysis into 11-amino undecanoic acid.
The applicant has since continued work on the processes for synthesis of these higher monomers, based on the use of natural oils which are sources of oleic, ricinoleic, lesquerolic, erucic or other acids. The applicant, accordingly, has explored a pathway wherein the acid function was converted during the process into nitrile function by nitrilation (ammonization) and then, after introduction of an acid or ester function into the molecule, by oxidative cleavage or metathesis with an acrylate, was reduced to primary amine function at the end of the conversions. This is the context in which the applicant filed a patent application, WO2010/055273, covering different versions of implementation of the process, all of them involving the formation of an ω-unsaturated fatty nitrile.